The ultimate goal of these studies is to enhance the brain delivery of drugs across the blood brain barrier (BBB) using a novel drug delivery system, poly(ethylene oxide)-poly(propylene oxide) block copolymers (Pluronic) or "poloxamer"). In vitro and in vivo studies completed in the previous grant, have demonstrated that Pluronic inhibits P-glycoprotein (Pgp), and enhances transport of Pgp substrates across the BBB to the brain. The mechanisms of Pluronic effects in BBB are not well understood. Therefore the objective of this proposal is to determine the mechanisms through which Pluronic affect drug transport systems in the BBB and to identify Pluronic formulations that have potential for drug delivery to the brain. Based on preliminary data, the hypothesis being evaluated is that Pluronic causes a) energy depletion and b) membrane fluidization in brain microvessel endothelial cells, which can affect various drug transport mechanisms in BBB, thus altering delivery of drugs affected by these mechanisms to the brain. Using brain microvessel endothelial cells as an in vitro model of the BBB, and using in vivo tissue sampling in mice, the Specific Aims of the proposed studies are to: (1) Characterize the mechanism of Pgp inhibition by Pluronic in BBB and evaluate the involvement of energy depletion and membrane fluidization in Pgp inhibition, (2) Examine the extent to which Pluronic effects on energy depletion and membrane micro viscosity can alter other transporters and carrier systems in BBB, (3) Examine the extent to which Pluronic effects on energy depletion and membrane micro viscosity can alter vesicular transport mechanisms in BBB and affect delivery of macromolecules across BBB through the vesicular transport route and, (4) Determine how formulation and pharmacokinetic parameters of Pluronic affect delivery of Pgp dependent drugs to the brain in vivo and identify factors critical for successful drug delivery to the brain using Pluronic.